Subject of the invention is an electromechanical measuring converter pin, particularly for measuring force of varying influence line.
The most frequently measured quantity in the industrial practice is the force. Along the propagation of the electrical measuring methods several solutions have been worked out for the conversion of force to electric signal. The strain gauge type measuring converters are recently the most frequently used for this purpose, which however utilize other physical phenomena as well. In these electromechanical measuring converters the correct conversion of the force to electric signal requires the coincidence of the influence line of the force to be measured and the measuring direction of the converter. In every other case additional stresses are produced in the measuring body in the wake of the additional load. While the force applied on the measuring body is a single force, the measuring converter produces from this resultant force an electric signal proportionate to the component in the measuring direction. If moment too arises as resultant, then the converter measures component corresponding to force even from this moment.
Consequently careful attention is paid in the practice to the correct introduction of the force. Special structural elements are provided for taking up the force perpendicularly to the measuring direction in order to prevent its effect on the measuring body of the converter, i.e. to prevent the development of forces deviating from the measuring direction. The problem was solved with the development of the holder type force meter. Later measuring shaft or pin type converters were used for this purpose. In spite of this diversified construction, in addition to the absolute value of the force to be measured its influence line too will inevitably vary in the several measuring tasks.
Each measuring converter used so far produces electric signal proportionate only to the component in the measuring direction. Such is for example the construction according to the Soviet patent specification No. 198 735. Actually this is a holder, supported on both ends. Between these two supports two truncated cones are arranged with their large diameter bases turned against each other. The double cone is loaded by concentric force along the large diameter part from the cylindrical bush. Thus this holder is exposed to bending load. The load can be increased until the generatrices of the cones will be parallel with the generatrix of the bush, i.e. when they bear upon each other.
Similar pin type force meter is described in the Swedish Pat. No. 311 573 or U.S. Pat. No. 3,554,025.
The measuring body is a holder clamped on both ends, and a moment and a force are applied to one of the ends. The moment too is produced by the force to be measured. The build-up of the measuring bridge is such that it is insensitive to the lateral force, i.e. it measures only the force in the direction of the vertical axis (coinciding with the force to be measured) of the sectional area of the measuring body. Consequently for the correct operation of the measuring converter the orientation of the converter in relation to the force to be measured is essential (e.g. during the measurement of funicular forces).
According to another method (GFR Pat. No. 24 35322) the force to be measured and the reaction force are applied as a couple of forces to both ends of the tubular shaft, thus the tubular shaft holder is exposed to permanent moment between the two intermediate positions of the force transfer. The measuring sensors however are arranged on the two ends of varying moment along the plane of the neutral strand at .+-.45.degree. to the direction of the shear stresses.
This way the measuring converter allows the measuring of the force component perpendicular to the neutral plane of the tubular shaft.
Similarly a couple of forces is formed on both ends of the holder by the measuring converter according to the GFR patent specification No. 2 631 698. In each of the different sectional areas the deformation sensor is arranged on the tangential surface perpendicular to the neutral plane, the measuring direction pointing to the direction of the tensile or compressive stresses produced by the shear stresses.
An interesting method is described in the GFR disclosure No. 2 650 442. According to this method one of the two perpendicular components of the force arising in the machine unit--bar, cylinder, etc.--along a straight line connecting two hinges in the mechanism of the power machines, such as elevator. The measuring body is trunnion-shaped and multisupported (three) holder, and each support may be conceived as a clamp. The two extreme clamps represent for example the reaction force, and the intermediate one represents the force to be measured. The neutral axis of the sectional area of the bent bar coincides with the direction of the component not to be measured, while the direction of the axis perpendicular to the former one is the direction of the measuring axis.
The measuring trunnion described in the Hungarian patent application No. VA-1538 realizes also the measuring of a unidirectional force. If the influence line of the force deviates from the line perpendicular to the plane determined by the longitudinal axis of the torsional parts of the measuring body, then the converter will measure the force component in the direction of the perpendicular line.
In the Soviet copyright certificate No. 140 593 such measuring trunnion is described, which allows the determination of the force applied to the shaft of the mechanisms. The measuring converter is a holder supported on both ends and loades in the centre. The load produced by the force to be measured is sensed in the direction of two axes perpendicular to each other and to the longitudinal axis of the holder, thus the force to be measured is divided into two components. According to the described method grooves are formed along the length of the cylinder at the two diameters of the sectional area, where the deformation sensors are arranged on the bottom of the surfaces.
The moment as the product of the force components and the spans produce the output signals of the measuring bridges.
The actual force is obtained by squared addition and square root extraction, its direction in relation to the two axes is obtained with arc tg function calculation.